chore(proxy): add CS_REGION to test.yml

CS_REGION is an env var required by the latest cipherstash-client
release.

Author: freshtonic

.github/workflows/test.yml

@@ -26,6 +26,7 @@ jobs:
           CS_DEFAULT_KEYSET_ID: ${{ secrets.CS_DEFAULT_KEYSET_ID }}
           CS_CLIENT_ID: ${{ secrets.CS_CLIENT_ID }}
           CS_CLIENT_KEY: ${{ secrets.CS_CLIENT_KEY }}
+          CS_REGION: "ap-southeast-2.aws"
 
           RUST_BACKTRACE: "1"
         run: |